The present invention concerns a method of producing flexible plastic bands formed of thermoplastic synthetic resins (for example of ethylene vinyl acetate copolymers) containing 40% or more by volume hard-material powder and/or soldering powder and 30% or less by volume plastic, the remainder being pores, by kneading the kneadable plastic with the hard-material powder and/or soldering powder at rather high temperatures. More particularly, the present invention relates to the above method wherein the components are placed (individually or as a granulate of the premixed components) onto two heated, grooved shearing rollers which are arranged parallel to one another and which run in opposite directions at different speeds.
In another aspect the present invention relates to flexible plastic band formed of thermoplastic synthetic resins (e.g., ethylene vinyl acetate copolymers) containing 40% or more by volume hard-material powder and/or soldering powder and 30% or less by volume plastic, the remainder being pores.
Methods of producing hard-material layers on metallic bases are known in which flexible plastic fleeces or films, containing hard materials and/or soldering powder, are placed on the bases and heated under a vacuum or under protective gas to temperatures at which the plastic decomposes without residue and the solder becomes liquid. The decomposition of the plastic creates a porous hard-material body whose pores are filled by the liquid solder, which brings about at the same time the bonding of the hard-material layer to the metallic base.
Such plastic fleeces or layers, which either separately contain hard-material particles and soldering powder or both powder types together, preferably consist of an ethylene vinyl acetate copolymer. They normally contain more than 40% by volume hard materials and/or solders and less than 30% by volume plastic. They preferably also contain 15 to 35% by volume pores.
Such fleeces or films and their manufacture are described, for example, in DE 38 01 958 . Thus, the hard materials and/or soldering powder can be introduced into the plastic in that the plastic is softened and rendered viscous with a solvent in order to then add the hard-material particles and/or soldering-powder particles in a kneading machine. The mass produced in this manner is then rolled flat and the solvent expelled. If a heated kneading machine is used the work can also be performed without solvent in that the thermoplastic qualities of the plastic are utilized. These methods have the disadvantage that inhomogeneities and fluctuations of density within the fleeces readily occur on account of the volumetrically large amounts of hard materials and/or soldering powder.
Shearing roller mills like those described for example in EP 0,231,398 and EP 0,148,966 are known for mixing, homogenizing and plastifying plastics. They consist of two tempered rollers which are arranged parallel to one another, rotate in opposite directions at different circumferential speeds and are provided with sharp-edged grooves which comminute the material and transport the plastic from the one front side of the rollers, the application side, to the other front side, the removal side.
However, the method parameters described in the above patent documents are not suited for mixing and plastifying plastic masses which volumetrically contain more solids than plastifiable plastics.